Phenotyping Summer Dormancy in Tall Fescue

Summer dormancy enables tall fescue (Festuca arundinacea Schreb.) to survive hot and dry summers. Phenotyping summer dormancy in the field can be problematic owing to the confounding effects of heat and drought. The objective therefore was to develop a method for phenotyping summer dormancy in tall fescue. Three genotypes (summer active [SA], moderately summer dormant [MSD], and strongly summer dormant [SSD]) were grown in four growth chambers under long day (LD) and high temperature (HT), LD and optimum temperature (OT), short day (SD) and HT, and SD and OT conditions. Within each chamber, two levels of moisture (well watered [+W] or drought [-W]) and vernalization (vernalized [+V] or nonvernalized [-V]) were also tested. Under SD, OT, +W, and +V conditions, SSD had equal or greater growth compared to SA genotype, as measured by number of tillers, plant height, fresh weight, and dry weight. The SSD genotype grew less than the SA as measured by number of tillers (8.6 vs. 15.8), fresh weight (6.0 vs. 16.0 g), and dry weight (3.1 vs. 8.8 g) under LD, OT, +W, and +V conditions. The MSD genotype had intermediate responses. Plant height of genotypes followed a similar pattern during two consecutive regrowth periods. Dormancy of plants could not be classified under drought or without prior vernalization. Dormancy of genotypes could be differentiated by comparing growth under favorable (SD, OT, +W, and +V) versus LD, OT, +W, and +V conditions.